Offset & Backspace - How Do They Relate? - Team Camaro Tech
Wheels & Tires What fits what?

 
LinkBack Thread Tools Display Modes
post #1 of 5 (permalink) Old Mar 31st, 11, 08:45 AM Thread Starter
Probationer
Discount Tire
 
Join Date: Jan 2011
Location: USA
Posts: 73
Offset & Backspace - How Do They Relate?

Offset and backspace are essentially two different ways of looking at the same thing. They determine the location of the wheel and tire assembly when bolted to the vehicles hub.

Offset is the measured distance between the hub mounting surface and the wheels center line.
With X being the determined offset, the hub mounting surface on positive offset wheels is X amount forward from the wheel center line. The hub mounting surface on negative offset wheels is X amount backwards from the wheel center line. The hub mounting surface on 0 offset wheels is the wheel center line.
Backspacing is the measurement from the hub mounting surface to the back edge of the wheel.

***Typically speaking, the higher the offset/backspace, the more the wheel will tuck inwards towards the suspension or away from the fender. The lower the offset/backspace, the more the wheel will push out away from the suspension or towards the fender.
For Example:
*If the offset on a 9" wide wheel is +12mm, the hub mounting surface will be 12mm forward from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 5.5"
*If the offset on a 9" wide wheel is -12mm, the hub mounting surface would be 12mm towards the back of the wheel from the wheels center line. Measuring from the hub mounting surface to the back edge of the wheel, the backspacing is 4.5"
Here's how to calculate the backspacing using the rim width and offset:
First - add 1" to the rim width and then divide by 2 to find the wheels center line (you have to account for the wheel flange which is why you add 1" to the rim width) . Second - convert the offset which is in millimeters into inches. There is 25.4mm in 1 inch so divide the offset by 25.4. Lastly - add the converted offset to the wheels center line if the offset is positive for the correct backspacing. Subtract the converted offset to the wheels center line if the offset is negative for the correct backspacing.
For Example:
17x9 +12mm offset
*9" rim width + 1" = 10"
*10"/2 = 5" (wheels center line)
*+12mm offset/25.4 = 0.47" (0.50" rounded up)
*0.50" + 5" = 5.50" Backspace

17x9 -12mm offset
*9" rim width + 1" = 10"
*10"/2 = 5" (wheels center line)
*-12mm offset/25.4 = 0.47" (0.50" rounded up)
*0.50" - 5" = 4.50" Backspace
***Please note that the wheels center line is the backspacing for 0 offset wheels.

I hope this helps.

-Matt

Low Prices! More Choices! Trusted Experts!
At The Store:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To Your Door:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Discount Tire is offline  
Sponsored Links
Advertisement
 
post #2 of 5 (permalink) Old Mar 31st, 11, 08:57 AM
Senior Tech
Steiner
 
Join Date: Mar 2009
Location: Lyman, SC
Posts: 8,348
Re: Offset & Backspace - How Do They Relate?

This helps even more. Used it when I got my Old School rims from you guys.




'69 Camaro
Dart 400-AFR 195-224/224 HR-Powerjection III TB with F.A.S.T. Sportsman XFI
TKO 600-Moser 3.42-Detroit Truetrac
500hp/538lbft

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

'69 Camaro Beater-SFT 327-M20-Moser 4.10-sold
'02 Z/28 vert-stock-sold and totaled
Steiner is offline  
post #3 of 5 (permalink) Old Mar 31st, 11, 09:00 AM Thread Starter
Probationer
Discount Tire
 
Join Date: Jan 2011
Location: USA
Posts: 73
Re: Offset & Backspace - How Do They Relate?

^
That works too! All the math is done for you

Low Prices! More Choices! Trusted Experts!
At The Store:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

To Your Door:
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Discount Tire is offline  
 
post #4 of 5 (permalink) Old Mar 31st, 11, 09:27 AM
Gold Lifetime Member
Matt
 
Join Date: Dec 2008
Location: Denver, CO
Posts: 3,120
Re: Offset & Backspace - How Do They Relate?

Well explained and some really good future reference.

Matt

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

zlek131 is offline  
post #5 of 5 (permalink) Old Mar 31st, 11, 10:24 AM
Tech Team
Mikko
 
Join Date: Mar 2009
Location: Finland
Posts: 91
Re: Offset & Backspace - How Do They Relate?

Yeah, this deserves to be a sticky Good post!

-1968 Camaro RS-
FinnRS is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome